Severe Weather Threat Day 1 Sat Aug 24

Models Continue To Indicate That Subtropical Ridging Will Become
Increasingly Prominent During This Period...With Anticyclonic
Mid/Upper Flow Encompassing Much Of The U.S. And Southern
Canada...Around A Strengthening High Center Over Missouri.

General Mid-Level Height Rises Across Parts Of The Northern Rockies Into The Northern Plains Likely Will Be Tempered... Somewhat...By The Continued Northeastward Progression Of A Short Wave Impulse Within The Monsoonal Regime Around The Periphery Of The High.

Additional...More Subtle...Convectively Generated Or Enhanced
Impulses Also May Continue To Stream Northward Into The Southern
Plateau And Great Basin...In Advance Of Tropical Storm Ivo.

At The Same Time...Large-Scale Upper Troughing Will Persist Across
The Eastern Pacific Into Pacific Coastal Areas. Several Significant
Short Wave Troughs Are Embedded Within This Regime...Including One Forecast To Migrate Inland Across British Columbia...And Another
Forecast To Take On An Increasingly Negative Tilt As It Approaches
The California Coast.

In Response To The Ongoing And Prior Upper Developments...Warm
Elevated Mixed Layer Air Is In The Process Of Advecting Northeast Across Much Of The Central And Northern Plains. This Air Mass Is Expected To Continue To Gradually Nose Into And Through The Upper Mississippi Valley During The Day Today...Above A Return Flow Of Seasonably Moist Air.

While The Leading Edge Of A Cool/Dry Intrusion Progresses South Through Southern Atlantic Coastal Areas...And Drying Occurs Across Parts Of The Central/Southern High Plains As Low-Level Flow Takes On An Increasing Southwesterly Component There...Seasonably High Moisture Content Air East Of The Rockies Will Otherwise Become Increasingly Confined To The Gulf Coast Region.

West Of The Rockies...Increasingly Moist Air Will Continue To Advect Northward From The Gulf Of California...And The Lower Latitude Eastern Pacific...Into The Southern Plateau...Eastern Great Basin...Central And Southern Rockies.

Northern Plains/Upper Mississippi Valley...

With Surface Heating Beneath The Capping Elevated Mixed Layer
Air...Large Boundary Layer Cape Appears Likely To Develop Across
Much Of The Region During The Day. It May Not Be Out Of The
Question That Lower/Mid Tropospheric Warm Advection On The Eastern Edge Of The Stronger Capping Could Support Scattered Convective Development...From Parts Of Western Minnesota At Midday Into The Upper Great Lakes Region By Early Evening.

However...It Currently Seems More Probable That General Warming From West To East Will Tend To Suppress Convective Development... With The Primary Convective Potential Developing In Association With The Upper Impulse Progressing Northeast Of The Rockies Into Western North Dakota By Late Afternoon.

Lift...Along With A Belt Of Enhanced Flow Accompanying This Feature ...Will Provide Support For The Evolution Of An Organized Convective System...Which Could Spread Across Much Of Central And Northern North Dakota Into Northwestern Minnesota By Late Evening.

With The Boundary Layer Expected To Become Hot And Deeply Mixed In Advance Of The Convection Across Much Of This Region... Thermodynamic Profiles Should Be Favorable For Downbursts And Strong Cold Pool Development...Accompanied By The Risk For Severe Surface Gusts.

Snake Valley And Adjacent Northern Intermountain Region...

Thermodynamic Profiles Are Forecast To Become Characterized By A
Deeply Mixed Boundary Layer...With Large Temperature/Dew Point
Spreads...And Sizable Cape By Late Afternoon. This Environment
Should Be Supportive Of At Least Low Potential For Severe Wind
Gusts...In Scattered Thunderstorm Development Expected In Response To Forcing For Upward Vertical Motion...Downstream Of The Trough Approaching The Pacific Coast.

Arizona...

Timing Of Potential Upper Impulses Impacting The Phoenix Metro Area And Adjacent Lower Deserts Remains Unclear. However... Forecast Soundings Indicate The Development Of A Hot And Fairly Moist...But Deeply Mixed...Boundary Layer With Sizable Temperature /Dew Point Spreads And Weak To Moderate Cape By Late Afternoon.

This Should Support At Least Low Potential For Severe Wind Gusts With Any Clustering Of Convection Developing Northward Across The
Region...Within Generally Weak Deep Layer Southerly Mean Flow.


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